Conventionally, playback of music or video images by controlling synchronization of a plurality of playback apparatuses, which are connected with each other via communications network such as Ethernet (registered trademark) and which process and play audio data and/or video data has been conducted.
When video frames are synchronized among playback apparatuses which are connected with each other via a communications network, a high degree of accuracy is required. Therefore, a hardware technique is employed such that a reference synchronization signal, generated using an external synchronization signal generator such as a Genlock (Generator Lock) circuit, is inputted into the plurality of playback apparatuses, and then synchronized (see Patent Literature 1).
In order to eliminate the need for an external circuit such as a synchronization signal generator, there is a technique in which a transmitter and receivers that are connected via a communications network cyclically generate a reference synchronization signal and secondary synchronization signals, respectively, thereby establishing frequency synchronization between a reference clock of the transmitter which serves as a basis for synchronization and local clocks of the receivers which are to be synchronized. The transmitter transmits a video timing packet to the receivers based on the reference clock. The video timing packet includes information relating to a difference in timing between a time at which the video timing packet has been transmitted to the communications network and a time at which the reference synchronization signal has been generated. Each receiver controls a timing at which the secondary synchronization signal is generated, based on the information included in the video timing packet relating to the difference in timing between the time at which the video timing packet has been transmitted to the communications network and the time at which the reference synchronization signal has been generated, as well as based on a time at which the timing packet has arrived (see Patent Literature 2).
Furthermore, in accordance with the spread of network-connected home appliances, technology for controlling synchronization of various home electric appliances that are connected via a communications network as well as of playback apparatuses for audio data and/or video data, at low cost, is also desired.